The Army may still march on its stomach, as Napoleon said, but its exercise regimen for abs is no longer absolute.

In fact, all the armed services - except for the Army - have abandoned the sit-up in favor of a less back-wrenching abdominal exercise known as the "curl-up," or "crunch." And pressure is mounting on the Army to do the same.

Traditionalists are holding firm as a washboard, however.

"We haven't seen anything that would cause us to make a service-wide change," says Major Tom Collins, an Army spokesman who can do some 82 sit-ups in a two-minute period. "Personally I've never had a problem with it, and I never knew anyone who did."

Sinewy debate

But some experts say the curl-up is simply a better exercise, not simply a fad of today's Richard Simmons/Suzanne Somers era.

The curl-up, in which one crosses one's arms over the chest, eases strain on the lower back by keeping it flat to the floor. It also does a better job isolating the stomach muscles - although the benefits of that remain in dispute.

In the Army sit-up, however, the hands must be behind the head, and the elbows must be lifted to the raised knees. In addition to working the stomach muscles, the sit-up exercises the hip-flexors. And, some say, it hurts.

"The downside [to the sit-up] is that you exert pressure on the back, and that can be harmful," says James Hodgdon, a research physiologist at the Naval Health Research Center in San Diego, Calif.

Mr. Hodgdon, who helped the Navy and Marines phase the sit-up out of their exercise routines in favor of the curl-up, thinks the Army should follow their lead.

But, he says, there is little more than anecdotal evidence suggesting that the sit-up is bad for the back, making it difficult for the Army to justify the change.

"There may be an element of tradition involved," he says, "but that is coupled with a lack of proof of a problem."

While the controversy remains mild, the topic has still become surprisingly sensitive for the Army.

National-security alert!

One official worried about potential enemies obtaining US exercise secrets, and urged the press to maintain a high level of discretion when writing about sit-ups.

Privately, however, some Army experts have questioned the value of the sit-up, as well as the entire exercise regimen.

One, who asked to remain anonymous, suggested that US soldiers would be better off doing stomach exercises that encouraged greater flexibility.

"I rarely do sit-ups as they're done in the Army," an Army instructor says. "I prefer to use a medicine ball."

Another point of sit-up contention is the speed at which they are done.

Army soldiers are tested every six months to see how many they can complete n a 2-minute period. They are awarded points based on age and number of sit-ups.

Don't rush it

The problem with that, according to one outside observer, is that a proper sit-up should be done slowly, with a greater emphasis on form than on speed.

"You're more apt to hurt your back if you do it fast," says Clarence Bass, a physical fitness expert based in Albuquerque, N.M. "It should be done slowly and methodically."

But Mr. Bass, the author of eight books about fitness, does not necessarily think that the Army is wrong to keep the old-school sit-up as part of its training regimen. The value of it, he says, is that it exerts the hip-flexor muscles, which may improve a soldier's all-around mobility.

Nonetheless, he also stands behind the crunch.

"The best would be to use each one [the sit-up and the crunch] some of the time," says Mr. Bass. "They're both boring."

Another independent fitness expert agrees that the sit-up is neither useless nor detrimental.